Studying Characteristics and Strength of the Unsaturated Gypseous Soil with Various Saturation Degrees

Abstract

Tests on gypseous soil include standard Proctor compactions and consolidated undrained triaxial compression.• The soil was either natural, unsaturated at degrees of saturation (30%, 60%, and 80%), or fully saturated. • Increasing the humidity of the gypseous soil at saturation degrees causes a decline in the internal friction angle. • The soil cohesion for effective and total stress increased with gypseous soil moisture up to (60%) saturation degree.The main objective of this study is to determine the appropriateness of unsaturated gypseous soil as a subgrade layer for carrying foundations. A comprehensive laboratory testing program was implemented to investigate the geotechnical characteristics and behavior of unsaturated gypseous soil. Tests that are physical included specific gravity, classification tests, relative density, Proctor compactions, single and double oedometer collapse potential, and static triaxial compression (CU-test). Chemical testing, Scanning Electron Microscopy (SEM), and Electronic Dissipation x-ray Scanning (EDS) analyses were also carried out.The tests were performed for samples prepared at 70% relative density of the natural gypseous soil. Tests are performed on the natural, unsaturated at degrees of saturation (30%, 60%, and 80%) and fully saturated gypseous soil to investigate the gypseous soil behaviors. In both single and double oedometer testing, it was discovered that the degree of specimen collapse is (Moderate) at 70% relative density, with a collapse index value ranging from (4%). The angle of internal friction for both total and effective stresses (φ' and φ) decreases as the moisture content of the gypseous soil increases at all saturation levels. In contrast, it was found that the strength of soil cohesion for both total and effective stresses (c' and c) increased with increasing gypseous soil moisture up to saturation (60%), which led to a rise in soil shear strength. The reduction value ranged from (38.50° to 7°) in respect of effective stresses and between (34.50° and 7°) with respect to total stresses. Effective stress increase varied from (10.0 -26.0 kPa), and total stress increase ranged from (12.50 -28.0 kPa). Then the strength started gradually decreasing at the saturation degrees 80 and 100%, respectively. As a result, the shear strength of the soil decreases with the value of reduction ranging from (20.0 -11.50 kPa) for effective stresses and (21.50 -11.50 kPa) for total stresses.

Effect of Initial Water Content on the Collapsibility of Natural and Cement-Treated Gypseous Soils

“…Comparison between silica-fume and nano-silica fume on improving the collapsibility and shear strength of soil with high gypsum ratio [6]. The treatment of soil containing different amounts of gypsum by sodium silicate was studied by [7]. It was concluded that the collapse potential of the treated gypseous soil decreases with the increase in ratio of sodium silicate.…”